Merge pull request #6 from nathan7/no-extensions

remove the (entirely useless) remnants of the extension system
Merge pull request #7 from nathan7/pledge

Total rewrite derived from nathan7/pledge.
Shorthand for github dependencies

npm tends to do a better job this way
I don't like void
I like a var per variable
Revert "depend on nathan7/next-tick for now"

This reverts commit 845154ad01ca941554f9442c40f2c72256f28fd9.
timoxley/next-tick#5 got merged so there's no need to depend on the
fork.